The present invention relates to a roller bearing cage that is made of a resin and is used for a roller bearing and a tapered roller bearing that uses the roller bearing cage.
A cage, which is incorporated in a tapered roller bearing used in a transmission device or a differential device of a vehicle, an axel of a railroad vehicle or an industrial machine, or a tapered roller bearing of a hub unit bearing disclosed in Patent Document 1, is made of a resin material that has smaller weight than a metal material and excellent productivity and economical efficiency. Generally, the cage that is made of the resin material includes a large-diameter annular portion and a small-diameter annular portion that are concentrically disposed on opposite sides of the cage in an axial direction, and a plurality of pillar portions that extend between the large-diameter annular portion and the small-diameter annular portion at a plurality of locations in a circumferential direction. In this cage, pockets are defined between the pillar portions. Meanwhile, in an assembling process of the roller bearing, for example, as shown in FIG. 7, after tapered rollers are inserted in the pockets of the cage, an inner ring member is pressed from an axial direction, and the tapered rollers are mounted in the pockets. At this time, the tapered rollers are forcibly fitted to the pockets by elastic deformation of the resin.
Patent Document 1; JP-A-11-044322
In the assembly process of the roller bearing, when the inner ring member is pressed and the tapered rollers are forcibly fitted to the pockets, an edge portion 60 of the tapered roller at an boundary between an outer circumferential portion and an end surface of the tapered roller at the small-diameter annular portion side presses and elastically deforms the small-diameter annular portion-side end 61 of the pillar portion (see FIG. 6A).
Meanwhile, in the tapered roller bearing that is used in the transmission device or the differential device of the vehicle, the cage comes into contact with lubricating oil, such as gear oil, which contains additives such as extreme-pressure additives, and thus it is required to use a resin having an oil resistance. Accordingly, the resin that forms the cage needs to have a high heat resistance and oil resistance. However, when a reinforcing material is mixed in the resin that has physical properties such as the heat resistance or oil resistance, the resin generally has high rigidity. When the resin having high rigidity is used, the strong stress may be applied to the pillar portions due to elastic deformation by the tapered roller, and a portion of the pillar portions may be damaged or cracked.
The above-described problems may occur when a rib is provided on the small diameter side of the inner ring member. In particular, as shown in FIGS. 1 and 7, in a tapered roller bearing where an outer ring angle, which is an angle of the outer ring with respect to an inner circumferential raceway surface, which corresponds to an angle α2 in FIGS. 1 and 7, is 20° or more, for example, in a range of not less than 20 and less than 30°, and a roller angle, which corresponds to an angle γ1 in FIGS. 1 and 7, is in a range of 7 to 10°, when the rollers are mounted in the cage and is assembled in the inner ring member, due to the rib provided on the small diameter side of the inner ring member, movement amount at the small diameter side of the roller that is pushed to the outside of the diameter direction is increased as compared with the case where the outer ring angle is less than 20° and the roller angle is in a range of 5 to 7°. As a result, the stress, which is applied to an end of the pillar portion at the small-diameter annular portion side, increases.
In order to solve the above-described problems, in regards to a material, an amount of a reinforcing material mixed in the resin material is reduced so as to improve flexibility of the resin. In this case, the strength or heat resistance may be lowered. Further, in regards to a shape, as shown in FIG. 6B, corners 72 of the pillar portions 70 and the small-diameter annular portion 71 on which the stress focuses are formed in a circular bore shape. In this case, since a mold structure for forming the cage becomes complicated, it becomes difficult to manufacture the cage.